1. Field of the Invention
The present invention relates to a planar type ferrite core to be attached to a coil pattern forming circuit board etc.
2. Description of the Related Art
Circuit boards are sometimes provided with so-called E-shaped planar type ferrite cores at parts of the circuit boards formed with coil patterns in order to mount transformers, inductors, and other coil devices (for example, see Japanese Patent Publication (A) No. 2003-151838).
An E-shaped planar type ferrite core generally has a rectangular flat part, a pair of outside legs projecting out from the two ends of the flat part in a-direction substantially perpendicular to the plane of the flat part, and a center leg positioned between the pair of outside legs and projecting out from the flat part in the same direction as the outside legs.
In such an E-shaped planar type ferrite core, in the past, the two ends of the center leg in the longitudinal direction were often made right angle surfaces. A coil pattern formed on the circuit board is formed by a pattern designed to surround the center leg. Therefore, if the two ends of the center leg are right angle surfaces, the coil pattern formed on the board would be wound around the right angle surfaces with great clearance and dead space would result.
In the days when reduction of the size of electronic devices including circuit boards was not demanded that much, these coil patterns did not pose any problem, but as power supplies have been reduced in size, they have come to be considered a problem. That is, there is fierce competition going on to improve the output current densities of power supplies even incrementally. Securing space for mounting electronic devices has become an element in development.
Further, in thin type power supplies used for planar type ferrite cores, reduction of the Joule's heat has become an important element in development in the same way in terms of improvement of the power efficiency.